function.c

早期freebsd实现

  p->cleanup_label = cleanup_label;
  p->return_label = return_label;
  p->save_expr_regs = save_expr_regs;
  p->stack_slot_list = stack_slot_list;
  p->parm_birth_insn = parm_birth_insn;
  p->frame_offset = frame_offset;
  p->tail_recursion_label = tail_recursion_label;
  p->tail_recursion_reentry = tail_recursion_reentry;
  p->arg_pointer_save_area = arg_pointer_save_area;
  p->rtl_expr_chain = rtl_expr_chain;
  p->last_parm_insn = last_parm_insn;
  p->context_display = context_display;
  p->trampoline_list = trampoline_list;
  p->function_call_count = function_call_count;
  p->temp_slots = temp_slots;
  p->temp_slot_level = temp_slot_level;
  p->fixup_var_refs_queue = 0;
  p->epilogue_delay_list = current_function_epilogue_delay_list;

  save_tree_status (p);
  save_storage_status (p);
  save_emit_status (p);
  init_emit ();
  save_expr_status (p);
  save_stmt_status (p);
  save_varasm_status (p);
}

/* Restore the last saved context, at the end of a nested function.
   This function is called from language-specific code.  */

void
pop_function_context ()
{
  struct function *p = outer_function_chain;

  outer_function_chain = p->next;

  current_function_name = p->name;
  current_function_decl = p->decl;
  current_function_pops_args = p->pops_args;
  current_function_returns_struct = p->returns_struct;
  current_function_returns_pcc_struct = p->returns_pcc_struct;
  current_function_needs_context = p->needs_context;
  current_function_calls_setjmp = p->calls_setjmp;
  current_function_calls_longjmp = p->calls_longjmp;
  current_function_calls_alloca = p->calls_alloca;
  current_function_has_nonlocal_label = p->has_nonlocal_label;
  current_function_contains_functions = 1;
  current_function_args_size = p->args_size;
  current_function_pretend_args_size = p->pretend_args_size;
  current_function_arg_offset_rtx = p->arg_offset_rtx;
  current_function_uses_const_pool = p->uses_const_pool;
  current_function_uses_pic_offset_table = p->uses_pic_offset_table;
  current_function_internal_arg_pointer = p->internal_arg_pointer;
  max_parm_reg = p->max_parm_reg;
  parm_reg_stack_loc = p->parm_reg_stack_loc;
  current_function_outgoing_args_size = p->outgoing_args_size;
  current_function_return_rtx = p->return_rtx;
  nonlocal_goto_handler_slot = p->nonlocal_goto_handler_slot;
  nonlocal_goto_stack_level = p->nonlocal_goto_stack_level;
  nonlocal_labels = p->nonlocal_labels;
  cleanup_label = p->cleanup_label;
  return_label = p->return_label;
  save_expr_regs = p->save_expr_regs;
  stack_slot_list = p->stack_slot_list;
  parm_birth_insn = p->parm_birth_insn;
  frame_offset = p->frame_offset;
  tail_recursion_label = p->tail_recursion_label;
  tail_recursion_reentry = p->tail_recursion_reentry;
  arg_pointer_save_area = p->arg_pointer_save_area;
  rtl_expr_chain = p->rtl_expr_chain;
  last_parm_insn = p->last_parm_insn;
  context_display = p->context_display;
  trampoline_list = p->trampoline_list;
  function_call_count = p->function_call_count;
  temp_slots = p->temp_slots;
  temp_slot_level = p->temp_slot_level;
  current_function_epilogue_delay_list = p->epilogue_delay_list;

  restore_tree_status (p);
  restore_storage_status (p);
  restore_expr_status (p);
  restore_emit_status (p);
  restore_stmt_status (p);
  restore_varasm_status (p);

  /* Finish doing put_var_into_stack for any of our variables
     which became addressable during the nested function.  */
  {
    struct var_refs_queue *queue = p->fixup_var_refs_queue;
    for (; queue; queue = queue->next)
      fixup_var_refs (queue->modified, queue->promoted_mode, queue->unsignedp);
  }

  free (p);

  /* Reset variables that have known state during rtx generation.  */
  rtx_equal_function_value_matters = 1;
  virtuals_instantiated = 0;
}

/* Allocate fixed slots in the stack frame of the current function.  */

/* Return size needed for stack frame based on slots so far allocated.
   This size counts from zero.  It is not rounded to STACK_BOUNDARY;
   the caller may have to do that.  */

int
get_frame_size ()
{
#ifdef FRAME_GROWS_DOWNWARD
  return -frame_offset;
#else
  return frame_offset;
#endif
}

/* Allocate a stack slot of SIZE bytes and return a MEM rtx for it
   with machine mode MODE.
   
   ALIGN controls the amount of alignment for the address of the slot:
   0 means according to MODE,
   -1 means use BIGGEST_ALIGNMENT and round size to multiple of that,
   positive specifies alignment boundary in bits.

   We do not round to stack_boundary here.  */

rtx
assign_stack_local (mode, size, align)
     enum machine_mode mode;
     int size;
     int align;
{
  register rtx x, addr;
  int bigend_correction = 0;
  int alignment;

  if (align == 0)
    {
      alignment = GET_MODE_ALIGNMENT (mode) / BITS_PER_UNIT;
      if (mode == BLKmode)
	alignment = BIGGEST_ALIGNMENT / BITS_PER_UNIT;
    }
  else if (align == -1)
    {
      alignment = BIGGEST_ALIGNMENT / BITS_PER_UNIT;
      size = CEIL_ROUND (size, alignment);
    }
  else
    alignment = align / BITS_PER_UNIT;

  /* Round frame offset to that alignment.
     We must be careful here, since FRAME_OFFSET might be negative and
     division with a negative dividend isn't as well defined as we might
     like.  So we instead assume that ALIGNMENT is a power of two and
     use logical operations which are unambiguous.  */
#ifdef FRAME_GROWS_DOWNWARD
  frame_offset = FLOOR_ROUND (frame_offset, alignment);
#else
  frame_offset = CEIL_ROUND (frame_offset, alignment);
#endif

  /* On a big-endian machine, if we are allocating more space than we will use,
     use the least significant bytes of those that are allocated.  */
#if BYTES_BIG_ENDIAN
  if (mode != BLKmode)
    bigend_correction = size - GET_MODE_SIZE (mode);
#endif

#ifdef FRAME_GROWS_DOWNWARD
  frame_offset -= size;
#endif

  /* If we have already instantiated virtual registers, return the actual
     address relative to the frame pointer.  */
  if (virtuals_instantiated)
    addr = plus_constant (frame_pointer_rtx,
			  (frame_offset + bigend_correction
			   + STARTING_FRAME_OFFSET));
  else
    addr = plus_constant (virtual_stack_vars_rtx,
			  frame_offset + bigend_correction);

#ifndef FRAME_GROWS_DOWNWARD
  frame_offset += size;
#endif

  x = gen_rtx (MEM, mode, addr);

  stack_slot_list = gen_rtx (EXPR_LIST, VOIDmode, x, stack_slot_list);

  return x;
}

/* Assign a stack slot in a containing function.
   First three arguments are same as in preceding function.
   The last argument specifies the function to allocate in.  */

rtx
assign_outer_stack_local (mode, size, align, function)
     enum machine_mode mode;
     int size;
     int align;
     struct function *function;
{
  register rtx x, addr;
  int bigend_correction = 0;
  int alignment;

  /* Allocate in the memory associated with the function in whose frame
     we are assigning.  */
  push_obstacks (function->function_obstack,
		 function->function_maybepermanent_obstack);

  if (align == 0)
    {
      alignment = GET_MODE_ALIGNMENT (mode) / BITS_PER_UNIT;
      if (mode == BLKmode)
	alignment = BIGGEST_ALIGNMENT / BITS_PER_UNIT;
    }
  else if (align == -1)
    {
      alignment = BIGGEST_ALIGNMENT / BITS_PER_UNIT;
      size = CEIL_ROUND (size, alignment);
    }
  else
    alignment = align / BITS_PER_UNIT;

  /* Round frame offset to that alignment.  */
#ifdef FRAME_GROWS_DOWNWARD
  function->frame_offset = FLOOR_ROUND (function->frame_offset, alignment);
#else
  function->frame_offset = CEIL_ROUND (function->frame_offset, alignment);
#endif

  /* On a big-endian machine, if we are allocating more space than we will use,
     use the least significant bytes of those that are allocated.  */
#if BYTES_BIG_ENDIAN
  if (mode != BLKmode)
    bigend_correction = size - GET_MODE_SIZE (mode);
#endif

#ifdef FRAME_GROWS_DOWNWARD
  function->frame_offset -= size;
#endif
  addr = plus_constant (virtual_stack_vars_rtx,
			function->frame_offset + bigend_correction);
#ifndef FRAME_GROWS_DOWNWARD
  function->frame_offset += size;
#endif

  x = gen_rtx (MEM, mode, addr);

  function->stack_slot_list
    = gen_rtx (EXPR_LIST, VOIDmode, x, function->stack_slot_list);

  pop_obstacks ();

  return x;
}

/* Allocate a temporary stack slot and record it for possible later
   reuse.

   MODE is the machine mode to be given to the returned rtx.

   SIZE is the size in units of the space required.  We do no rounding here
   since assign_stack_local will do any required rounding.

   KEEP is non-zero if this slot is to be retained after a call to
   free_temp_slots.  Automatic variables for a block are allocated with this
   flag.  */

rtx
assign_stack_temp (mode, size, keep)
     enum machine_mode mode;
     int size;
     int keep;
{
  struct temp_slot *p, *best_p = 0;

  /* First try to find an available, already-allocated temporary that is the
     exact size we require.  */
  for (p = temp_slots; p; p = p->next)
    if (p->size == size && GET_MODE (p->slot) == mode && ! p->in_use)
      break;

  /* If we didn't find, one, try one that is larger than what we want.  We
     find the smallest such.  */
  if (p == 0)
    for (p = temp_slots; p; p = p->next)
      if (p->size > size && GET_MODE (p->slot) == mode && ! p->in_use
	  && (best_p == 0 || best_p->size > p->size))
	best_p = p;

  /* Make our best, if any, the one to use.  */
  if (best_p)
    p = best_p;

  /* If we still didn't find one, make a new temporary.  */
  if (p == 0)
    {
      p = (struct temp_slot *) oballoc (sizeof (struct temp_slot));
      p->size = size;
      /* If the temp slot mode doesn't indicate the alignment,
	 use the largest possible, so no one will be disappointed.  */
      p->slot = assign_stack_local (mode, size, mode == BLKmode ? -1 : 0); 
      p->next = temp_slots;
      temp_slots = p;
    }

  p->in_use = 1;
  p->level = temp_slot_level;
  p->keep = keep;
  return p->slot;
}

/* If X could be a reference to a temporary slot, mark that slot as belonging
   to the to one level higher.  If X matched one of our slots, just mark that
   one.  Otherwise, we can't easily predict which it is, so upgrade all of
   them.  Kept slots need not be touched.

   This is called when an ({...}) construct occurs and a statement
   returns a value in memory.  */

void
preserve_temp_slots (x)
     rtx x;
{
  struct temp_slot *p;

  /* If X is not in memory or is at a constant address, it cannot be in
     a temporary slot.  */
  if (x == 0 || GET_CODE (x) != MEM || CONSTANT_P (XEXP (x, 0)))
    return;

  /* First see if we can find a match.  */
  for (p = temp_slots; p; p = p->next)
    if (p->in_use && x == p->slot)
      {
	p->level--;
	return;
      }

  /* Otherwise, preserve all non-kept slots at this level.  */
  for (p = temp_slots; p; p = p->next)
    if (p->in_use && p->level == temp_slot_level && ! p->keep)
      p->level--;
}

/* Free all temporaries used so far.  This is normally called at the end
   of generating code for a statement.  */

void
free_temp_slots ()
{
  struct temp_slot *p;

  for (p = temp_slots; p; p = p->next)
    if (p->in_use && p->level == temp_slot_level && ! p->keep)
      p->in_use = 0;
}

/* Push deeper into the nesting level for stack temporaries.  */

void
push_temp_slots ()
{
  /* For GNU C++, we must allow a sequence to be emitted anywhere in
     the level where the sequence was started.  By not changing levels
     when the compiler is inside a sequence, the temporaries for the
     sequence and the temporaries will not unwittingly conflict with
     the temporaries for other sequences and/or code at that level.  */
  if (in_sequence_p ())
    return;

  temp_slot_level++;
}

/* Pop a temporary nesting level.  All slots in use in the current level
   are freed.  */

void
pop_temp_slots ()
{
  struct temp_slot *p;

  /* See comment in push_temp_slots about why we don't change levels
     in sequences.  */
  if (in_sequence_p ())
    return;

  for (p = temp_slots; p; p = p->next)
    if (p->in_use && p->level == temp_slot_level)
      p->in_use = 0;

  temp_slot_level--;
}

/* Retroactively move an auto variable from a register to a stack slot.
   This is done when an address-reference to the variable is seen.  */

void
put_var_into_stack (decl)
     tree decl;
{
  register rtx reg;
  register rtx new = 0;